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31 Aug 2009

Volume 95, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 95, 091901 (2009); http://dx.doi.org/10.1063/1.3212896 (3 pages)

Noy Bassik, George M. Stern, and David H. Gracias
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Spatial variations in local switching parameters of ferroelectric random access memory capacitors

D. Wu, I. Kunishima, S. Roberts, and A. Gruverman

Appl. Phys. Lett. 95, 092901 (2009); http://dx.doi.org/10.1063/1.3192354 (3 pages) | Cited 5 times

Online Publication Date: 1 September 2009

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Spatially resolved studies of the switching behavior of micrometer scale Pb(Zr,Ti)O3 capacitors have been performed by piezoresponse force microscopy (PFM). PFM spectroscopy and bias-dependent imaging of domain patterns have been used to investigate variability in local switching parameters and address the capacitor scaling effect on switching. It was found that average coercive voltage and imprint bias are independent of capacitor size and are similar to the corresponding parameters obtained by polarization hysteresis measurements. This can be attributed to the slow switching kinetics during quasistatic PFM measurements. The obtained results demonstrate a possibility of testing the submicron capacitors in real devices.
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85.50.Gk Non-volatile ferroelectric memories
84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Imprint in ferroelectric materials due to space charges: A theoretical analysis

M. B. Okatan and S. P. Alpay

Appl. Phys. Lett. 95, 092902 (2009); http://dx.doi.org/10.1063/1.3222871 (3 pages) | Cited 11 times

Online Publication Date: 1 September 2009

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Imprint is a degradation mechanism in ferroelectrics that results in the displacement of the polarization hysteresis loop along the electric field axis. We develop a model using a nonlinear thermodynamic analysis coupled with electrostatics to show that such internal voltage offsets can originate from asymmetrically distributed trapped space charges. The electrostatic interactions are established through a built-in polarization due to the space charges and the spontaneous polarization. Numerical results for Ba0.8Sr0.2TiO3 show that the maximum electric field offset does not necessarily occur due to charges trapped near the electrodes.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

On-chip terahertz Goubau-line waveguides with integrated photoconductive emitters and mode-discriminating detectors

L. Dazhang, J. Cunningham, M. B. Byrne, S. Khanna, C. D. Wood, A. D. Burnett, S. M. Ershad, E. H. Linfield, and A. G. Davies

Appl. Phys. Lett. 95, 092903 (2009); http://dx.doi.org/10.1063/1.3216579 (3 pages) | Cited 4 times

Online Publication Date: 1 September 2009

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We have measured the picosecond time-domain response of Goubau-line waveguides, formed on quartz substrates, by integrating regions of low-temperature-grown gallium arsenide into the waveguides to act both as pulsed current emitters and detectors. Using one pair of photoconductive switches for excitation and a second pair for detection, pulsed signal propagation of a low dispersion electric field mode was demonstrated in the Goubau-lines, with the signal bandwidth extending beyond 800 GHz. Furthermore, it was demonstrated that terahertz bandstop filters can be integrated into a Goubau-line for removal of specific frequencies from the transmitted pulses.
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84.40.Az Waveguides, transmission lines, striplines
85.60.-q Optoelectronic devices

Mapping bias-induced phase stability and random fields in relaxor ferroelectrics

B. J. Rodriguez, S. Jesse, A. A. Bokov, Z.-G. Ye, and S. V. Kalinin

Appl. Phys. Lett. 95, 092904 (2009); http://dx.doi.org/10.1063/1.3222868 (3 pages) | Cited 6 times

Online Publication Date: 4 September 2009

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The spatial variability of polarization reversal behavior in the relaxor 0.9Pb(Mg1/3Nb2/3O3)–0.1PbTiO3 crystal, is revealed on the ∼ 100 nm scale using switching spectroscopy piezoresponse force microscopy. Quenched fields conjugate to polarization are found, which show mesoscopic ( ∼ 100–200 nm) spatial fluctuations around near-zero bias values. The mapping of the stability gap of the bias-induced phase and conjugate random fields is demonstrated. The origin of the observed nanoscale domains and the field-induced part of the polarization are discussed.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.07.Bc Nanocrystalline materials
77.80.B- Phase transitions and Curie point
77.80.Fm Switching phenomena

Universality in phase diagram of (K,Na)NbO3–MTiO3 solid solutions

Ruiping Wang, Hiroshi Bando, and Mitsuru Itoh

Appl. Phys. Lett. 95, 092905 (2009); http://dx.doi.org/10.1063/1.3224196 (3 pages) | Cited 9 times

Online Publication Date: 4 September 2009

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Detailed phase diagrams are necessary for improving the temperature stability of piezoelectric properties of (Na,K)NbO3-based solid solutions. We report the phase diagrams of the (1−x)Na0.5K0.5NbO3–xMTiO3 (M = Pb, Ba, Sr, Ca, and Bi0.5Li0.5) solid solutions over a broad temperature range of 10 K ≤ T ≤ ∼ 770 K. It is found that the phase diagrams show several universal characteristics: (a) Curie temperature TC-T decreases sharply at low x range; (b) the relation between TC-T and x deviates from Vegard’s law; and (c) the tetragonal-orthorhombic phase transition temperature TT-O and the orthorhombic-rhombohedral phase transition temperature TO-R are almost independent of M. We suggest that valence mismatch is the main reason for the rapid decrease in TC-T and the deviation of TC-T from Vegard’s law. It is also found that TC-T is mainly affected by the A-site cations, whereas TT-O and TO-R are mainly affected by the B-site cations.
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81.30.Dz Phase diagrams of other materials
77.65.-j Piezoelectricity and electromechanical effects
64.70.K- Solid-solid transitions
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